Changing information displays are commonly used, in particular related to commercials. Also in other areas, such as traffic signs, there is a need for the ability to change the information that is displayed, such as speed limits, re-routing information, closed roads, etc.
Today the most commonly used changeable displays/signs make use of LED or LCD. These types of displays, however, are not suitable in very light environments (such a bright sunshine) as they have too low contrast and visibility. This is particularly a problem with road signs.
It has earlier been suggested to use liquid-filled signs where the liquid can be filled or drained in order to change information, but such signs have so far not been successful, probably due to lack of flexibility, and leakage. SE 220629 describes an indication device for traffic, commercials, etc. which comprises a transparent board arranged with cavities which may be filled to be visible. This device needs backlight to be visible, has many pumps and sealings that can cause leakage and is not suitable for very low or very high temperatures.
U.S. Pat. No. 1,458,840 describes a sign with a sign plate pervious to light rays and a closed space defining a sign character. The space is filled with liquid by a plunger activated by an electro magnet and emptied by gravity through the same pipes. The signs are visible only when the electro magnet is active, thus demanding continuous power supply when the information is displayed.
EP 1862874 describes a display device fitted to a watch having cavities which may be filled by a fluid by means of a micropump and microvalves. The microvalves alternately pumps and sucks the fluid to fill and empty the cavities.